Fiber arrays impregnated with various polymers are well known. Typically, these take the form of short randomly distributed fibers or long continuous fibers either in mat, weave or knit form or in continuous form where adjacent fibers are parallel and generally continuous through the fabric. For the purpose of the present invention one or more fibrous layers made from fiber impregnated with a polymeric matrix and useful to form articles is known as a "prepreg". Forms of prepregs include impregnated woven fabric, felt mats, as well as unidirectional fiber web.
The use of high strength and cut resistance fibers have made such prepregs useful to make articles which are resistant to cutting and high speed impact from projectiles such as BB's, bullets, shells, shrapnel, glass fragments, and the like.
Fibers conventionally used include aramid fibers, fibers such as poly(phenylenediamine terephthalamide), graphite fibers, ceramic fibers, nylon fibers, glass fibers and the like. For these applications, the fibers are ordinarily encapsulated or embedded in a rigid matrix material and, in some instances, are joined with rigid facing layers to form complex composite structures.
Ballistic articles such as bulletproof vests, helmets, armor plate, and other military equipment, structural members of helicopters, aircraft, ships, and vehicle panels and briefcases containing high strength fibers are known.
U.S. Pat. No. 4,403,012 and U.S. Pat. No. 4,457,985 disclose ballistic-resistant composite articles comprised of networks of ultra-high molecular weight polyethylene or polypropylene fibers in matrices composed of olefin polymers and copolymers, unsaturated polyester resins, epoxy resins and other resins curable below the melting point of the fiber.
Particular reference is made to U.S. Pat. No. 4,457,985 at Col. 3, beginning at line 53 where it is disclosed that ballistic resistant articles can contain fibers formed as a felt, basket woven or formed into fabric in any of a variety of conventional techniques. Reference is made to techniques such as those described in U.S. Pat. No. 4,181,768 and M. R. Silyquist, et al., J. Macromol. Sci. Cheme., A7 (1) 203 et seq (1973).
Reference is made to ballistic resistance composite articles disclosed in U.S. Pat. Nos. 4,457,985; 4,501,856; 4,613,535 4,623,574; and 4,650,710. These patents consistently teach forming prepregs and composite structures in the manner reviewed above with regard to U.S. Pat. No. 4,457,985.
U.S. Pat. No. 4,309,487 discloses ballistic resistant laminates of polyethylene fibers where the film or fibers in each layer are unidirectionally oriented and at an angle to fibers in adjacent layers. The laminates are made in the absence of adhesive with each layer being at least 0.5 mils thick. A six inch by six inch square film laminate is disclosed in the Examples. Also, of interest is U.S. Pat. No. 4,079,161.
The teachings of theese patents are consistent with the general teaching of the art that articles made of composites having ballistic resistance should be based upon fiber having continuous length in the article. This is supported by teaching such as Williams, et al., The Impact Strength Of Fibre Composites, Journal Of Materials Science, Vol. 8, p. 1765-1787 (1973); and Silverman, Effect Of Glass Fibre Length On The Creep and Impact Resistance Of Reinforced Thermoplastics, Polymer Composites, Vol. 8, No. 1 pp. 8-15 (February, 1987).
Alesi, Aramid Fiber-Reinforced Ionemer, Polymer Engineering and Science, Vol. 18, No. 16, pp. 1209-1215 (December, 1978) discloses the use of chopped aramid fiber having a length of from one quarter to one-half inch for use in compression and injection molding. Ballistic performance of these composites was very poor.
Roylance, et al., Ballistic Impact Of Textile Structures, Textile Research Journal, pp. 34-41 (January 1973) discloses fiber behavior during ballistic impact. Reference is also made to Roylance, Influence to Fibre Properties on Ballistic Penetration of Textile Panels, Fibre Science and Technology, Vol. 14, pp. 183-190 (1981). There is a review of ballistic penetration resistance of textile panels. These references suggest that fabrics made from continuous fibers would be consistent with their goals of improved ballistic composite properties.
Finally reference is made to Laible, Ballistic Materials and Penetration Mechanics, Elsevier Scientific Publishing Company (1980). This text consistent with the other art indicates the desirability of continuous length fiber for use to attain ballistic resistance.